Propellent powder



Dec; 15, 1959 COFFEE 2,916,996

PROPELLENT POWDER Filed Feb. 29, 1956 SMOKE LE 35 GRAIN FOR NG POWDER BASE I v APPARATUS SOL/D HIGH I F I 6 1 EXPLOS/VE LIQUID 7 FILTER I SURFACE EXTRACTION I SOLVENT FOR HIGH EXPLOS/VE LIQUID FILTER I WATER SURFACE HARDENING SOLVENT M GRA'NS W PRODUCT INVENTOR. RALPH E. COFFEE depending upon large -.with the nitrocellulose to impart the high energy characteristic, but they have the objectionable feature of developing high breech pressures process similar to that United States. Patent I 2,916,996 7 PROPELLENT POWDER Ralph E. Colfee, Berkeley,

Mathieson Chemical Corporation, a corporation of Virginia Application February 29, 1956, Serial No. 568,945

4 Claims. (Cl. 102-98) to explosives and more having improved burn- Mo., assignor to Olin East Alton, 111.,

grain. The ballistic characteristics of such powders are double base high energy powders an improvement over quantities of nitroglycerine mixed when loaded in cartridges in quantities suflicient 'to impart high velocities to the projectile. Moreover, as pointed out in the above referred to patent, it is impossible to coat such powder grains satisfactorily with a deterrent to impart maximum progressive burning characteristics to the grain.

It is, therefore, an object of this invention to provide a smokeless powder adapted to burn'progressively and impart high velocities to projectiles at improved breech pressure levels. Another object of the invention is to provide a novel smokeless powder having improved burning characteristics which impart high velocities to pro jectiles withiless breech pressure than the heretofore available powders. Still another object of the invention is to provide a high energy smokeless powder containing particles of a solid high explosive having a deterrent coating on the surface thereof. Still another object of vthe invention is to provide a smokeless powder containing particles of a solid high explosive having an imp'rovedgravimetric density. A more specific object of the invention is to provide a smokeless powder grain having a nitrocellulose matrix with particles of a solid high explosive embedded therein having improved progressive burning characteristics. a

.The foregoing objects as well as others are accomplished in accordance with this invention, generally speaking, by providing a progressive burning powder having a core containing particles of a solid high explosive substantially uniformly dispersed in a smokeless powder base matrix, and an envelope of smokeless powder base surrounding the core which contains a lesser percentage by. weight of high explosive or is substantially devoid of high explosive particles. Thesmokeless powder base matrix may be composed of gelatinized nitrocellulose "or .gelatinized nitrocellulose mixed with nitroglycerine or any other suitable nitric ester of a polyhydric alcohol, such as for example, dinitroglycol.

The powder grains may be formed in'the first step of the process by any conventional method suitable for forming grains having particles of solid high explosives dispersed in a smokeless powder base matrix. Globular powder grains of high density may be formed by a disclosed by Schaefer in US. Patent 2,160,626 modified to the extent that solid particles of high explosives are suspended in the lacquer globule before it is hardened by removing the solvent. The grains having the particles of high explosive dispellent charge as high as 1000 have been prepared ice persed throughout their structure are then extracted with a suitable solvent for the smokeless powder matrix to erase the pits left in the surface by the removal of the particles of high explosive and to produce a grain having a substantially smooth surface. The grain may be coated with a suitable deterrent, if desired, to further improve the progressive burning characteristics of the grain.

Any secondary solid explosive which is incompletely solublein the other ingredients of the powder grain and develops greater energy upon burning than nitrocellulose may be utilized. Examples of such explosives are pentaerythritol, tetranitrate, trinitrotoluene, cyclonite (cyclotrimethylenetrinitramine), homocyclonite (cyclotetramethylenetetranitrate), tetryl and the like. Of these explosives, cyclonite" is preferred because of the pressure velocity relationship obtained with smokeless powders containing this material.

The solid high explosive may be extracted either with any suitable solvent for the high explosive which is also a solvent for the smokeless powder base matrix or with any suitable solvent for the high explosive which is not a solvent for the smokeless powder base. Examples of solvents which fall in the latter category are'ethyl alcohol, xylene, benzene, toluene, methyl alcohol, isoof the grain and the slurry'is agitated until theparticles of high explosive have been extracted therefrom. The

thickness of the envelope or outer shell from which the solid high explosive is extracted may be varied somewhat depending upon the particular ballistic characteristics desired but it should not be more than about A of the diameter or thickness of'the grain to provide a grain having high energy characteristics with attending low pressure characteristics.

It has been found that cartridges containing a proof the powder provided by this invention impart a much higher muzzle velocity to the projectile at lower breech pressures than cartridges having a propellent charge of smokeless powder having the particles of high explosive dispersed substantially uniformly throughout the grain including the outer shell. Moreover, by treating the powder grains after the high explosive has been extracted from the outer shell thereof with a suitable solvent for the smokeless powder base, such as for example, ethyl acetate, methyl ethyl ketorie and the like to case harden the surface of the grains'and pits therein, the gravimetric density of the powder grain is greater than that obtainable with powder grains having the high explosive distributed throughout the grain. For example, propellants having a gravimetric density in accordance with this invention whereas the maximum density heretofore obtained with powders of the other type containing an equivalent amount of solid high explosive per unit of weight has not been greater than about 0.940. The solid particles of high explosives do not migrate into the outer shell even during long storage periodsat elevated, temperatures so the powder is more ballistically stable than powders depending upon nitroglycerine for their high energy characteristics. i

the solid high explosive particles In order better to describe and further clarify the invention, the following are detailed descriptions of preferred embodiments thereof taken in connection with the drawing in which:

Figure lisa flow diagram illustrating the steps of the process of the presentinvention; and

Figure 2 is a cross-sectional view of a powder grain resulting from the process.

The process of the present invention can be carried out in conventional grain forming and treating apparatus.v The grains are formed from a mixture of a propellent powder base and a solid high explosive in any desired manner in standard grain forming apparatus 1. Ifthe process employed involves suspension in a nonsolvent medium, the powder grains are filtered from the liquid medium as indicated at 2 and the high explosive material at or near the surface of the grain is extracted as indicated at 3 with a solvent therefor carried in an aqueous medium. After the surface extraction of the high explosive from the powder grains, they are separated from'the liquid medium by filtration 4 or other suitable means and then suspended in an aqueous medium containing a solvent for the smokeless powder base. This treatment is continued until the grains are provided with a smooth imperforate surface layer of the powderbase. The surface hardening step is indicated generally at 5. The grains which have thus been extracted and surface hardened are then separated from the suspending medium and subsequently dried.

Example 1 About 75 parts by weight nitrocellulose having a nitrogen content of about 13.2 percent are added to about 1500 parts water in a suitable grain forming still indicated generally at 1 at a temperature of about 50 C. and the resulting slurry is agitated to suspend the nitrocellulose therein. About 94 parts by weight cyclonite are suspended in about 375 parts ethyl acetate having dissolved therein about 0.75 part diphenylamine as a stabilizer. This mixture is agitated to suspend the cyclo nite therein and the suspension is then added to the nitrocellulose-water slurry. The resulting slurry is agitated as it is heated to about 68 C. After the nitrocellulose has dissolved, about 3 parts of a protective colloid derived from animal protein or an equivalent amount of gum arabic or any other suitable protective colloid are added and the slurry is agitated until the lacquer formed by the dissolution of the nitrocellulose is broken up into globules of the desired particle size. About parts sodium sulfate dissolved in about 200 parts water are added to the slurry and agitation of the slurry is continued for about three hours while the temperature is gradually raised to about 99 C. to

remove the ethyl acetate and convert the globules of lacquer into hardened powder grains having cyclonite distributed substantially uniformly throughout each grain. The composition of such grains is about 55 percent cyclonite, about 44.5 percent nitrocellulose and about 0.5 percent diphenylamine. from the liquid medium by filtering or other suitable means as indicated at 2 in the drawing.

In ordere to remove a total of about 15 percent of the cyclonite from the powder grain and to limit the removal to the outer shell of the grain, about 200 parts by weight of the powder grains prepared above are agitated in about 1260 parts ethyl alcohol, at about 76 C. in a slitable vessel 3 until the alcohol is saturated with cyclonite. The resulting powder grains will contain about 42.5 percent cyclonite and all of this cylonite will be in the core of the grain with the outer shell of the grain being substantially devoid of any particle of cyclonite.

If desired, the foregoing extraction process may be modified by using amounts of solvent, such as ethyl al- These grains are separated the liquid by filtering or other suitable means.

means.

Example 2 In another embodiment of the invention, powder grains shaped in accordance with the process disclosed above and containing particles of cyclonite distributed substantially uniformly throughout the structure are extracted with acetone which is a solvent for the nitrocellulose as well as for the cyclonite. About parts of the powder grains are agitated in a solution ofabout 395 parts acetone and about 495 parts water for about 15 minutes at about 55 C. The powder grains are then separated from the liquid, phase by filtration or other suitable means 4 and washed with water to remove the last traces of the suspending liquid.

The powder grains extracted by either of the fore going processes are surface hardened as indicated at 5 by suspending them in a water medium having a solvent phase. About 100 parts by weight of the powder grains are suspended in about 400 parts water containing about 5 parts gum arabic. About 75 parts ethyl acetate are added to the suspension and the slurry'is agitated While the temperature is increased to about 70 C. A salt solution .may beadded at this point to help improve gravimetric and grain density in accordance with the process disclosed by Schaefer in US. 2,160,626. Agitation is continued at this temperature for about two hours after which time the surface of the powder grains will have been softened by the solvent, lost the pits therein ,andassumed a substantially smooth surface. The temperatureis gradually elevated to about 99 C. to remove the ethyl acetate, The grains are then separated from The gravimetric density of the grains is increased by this treatment. Grains having a gravimetric density of about 0.920 before extraction have a gravimetric density of about 1.000 after extraction of the cyconite and after surface treatment of the grains in accordance with this procedure.

The grains obtained in accordance with the present invention are well illustrated in Figure 2 of the drawing. As indicated, the grains are substantially non-porous and consist of a central core portion 6 throughout which discrete particles 7-of a high explosive material, such as cyclonite, are uniformly dispersed. The core portion of the grain is completely encased in a surrounding envelope 8 which is substantially smooth and imperforate and also free of significant amounts of the secondary explosive.

As an example of the improved ballistic properties of propellant grains formed in accordance with this procwere obtained:

Charge Pressure Velocity (grains) (p.s.l.) (IL/sec.)

407 Cyelonite Powder 51. 700 2. 634 50 a Cyclonlte Powder 145 53, 700 2. 582

These data show that a charge of a nitrocellulose base powder provided by this invention containing 40 percent cyclonite propelled the projectile at' a muzzle velocity greater than the muzzle velocity of the projectile propelled by the powders having 50 percent cyclonite dispersed substantially uniformly therein and at a breech pressure of 2000 pounds per square inch less than the breech pressure developed by the powder containing the 50 percent cyclonite. A similar improvement is obtained in accordance with this invention with propellents containing one of the other secondary solid explosives set forth hereinbefore and also with propellent grains containing particles of nitroguanidine.

As indicated hereinbefore the powder grains can be made by any suitable process and then extracted in accordance with this invention. For example, any suitable extrusion or casting process for shaping propellent grains containing a solid high explosive dispersed in discrete form therein can be utilized. In making powder in accordance with the preferred embodiment disclosed above, any other suitable non-solvent medium may be utilized in lieu of water and any other suitable solvent may be used instead of ethyl acetate. The solvent should be substantially immiscible with the non-solvent medium. Examples of suitable solvents include methyl ethyl ketone, isopropyl acetate, ethylformamide, methyl isobutyl ketone and the like. The powder grains after the surface treatment to remove the pits therefrom may be treated with a deterrent in accordance with any suitable procedure, such as for example, by the emulsion coating process disclosed by Wagner in US. Patent 1,924,967. Suitable deterrents include dibutyl phthalate, diphenyl phthalate, ethyl centralite and the like. The grains may also be coated with nitrocellulose if desired by any suitable procedure including the one disclosed in the Wagner patent US. 1,862,914.

Although the invention has been described in detail in connection with the preparation of powders containing cyclonite, other solid high explosives can be incorporated in powder and extracted in a similar manner, and it is to be understood that the purpose of this detail is solely for illustration and that modifications can be made in the embodiments without departing from the spirit and scope of the invention except as it is limited by the appended claims.

I claim:

1. A progressive burning smokeless powder grain comprising a core having a'matrix of a smokeless powder base containing particles of a solid high explosive distributed substantially uniformly therein, a substantially imperforate envelope enclosing said core of gelatinized smokeless powder base said envelope being substantially devoid of solid high explosive particles and having a substantially smooth, imperforate surface, and on said envelope a coating of a deterrent.

2. The product of claim 1 wherein said high explosive is pentaerythritol tetranitrate.

3. The powder grain of claim 1 wherein the core contains at least 15% by weight of the high explosive.

4. A process for making smokeless powder grains having improved velocity and breech characteristics comprising mixing particles of a solid high explosive with a smokeless powder base, shaping the resulting mass. into powder grains, subjecting the resulting grains to the action of a solvent for the high explosive until substantially all of the particles of high explosive in the outer shell of the grains have been dissolved in the solvent and removed therefrom, and thereafter maintaining the grains in an aqueous suspension of a solvent for the smokeless powder base until the surface of the grains has become substantially smooth.

References Cited in the file of this patent UNITED STATES PATENTS 1,906,675 Wagner May 2, 1933 2,425,854 Alexander Aug. 19, 1947 

1. A PROGRESSIVE BURNING SMOKE''ESS POWDER GRAIN COMPRISING A CORE HAVING A MATRIX OF A SMOKELESS POWDER BASE CONTAINING PARTICLES OF A SOLID HIGH EXPLOSIVE DISTRIBUTED SUBSTANTIALLY UNIFORMLY THEREIN, A SUBSTANTIALLY IMPERFORATE ENVELOPE ENCLOSING SAID CORE OF GELATINIZED SMOKELESS POWDER BASE SAID ENVELOPE BEING SUBSTANTIALLY DEVOID OF SOLID HIGH EXPLOSIVE PARTICLES AND HAVING A SUBSTANTIALLY SMOOTH, IMPERFORATE SURFACE, AND ON SAID ENVELOPE A COATING OF A DETERRENT. 